218 



KNOWLEDGE. 



June, 1913. 



The spectroscopic method can be extended to the poles and 

 to undisturbed regions of the surface, and there is the 

 possibility of examining the lines of different elements and 

 seeing whether they indicate the same velocity. The draw- 

 back of the method is that the linear velocity of rotation, even 

 at the Equator, is only two kilometres per second ; and though 

 this is doubled on comparing opposite limbs it can hardly be 

 determined by the spectroscope within about three per cent., 

 which means an uncertainty of nearly a day in the period. 

 The three most reliable series appear to be those of Adams, 

 Plaskett and DeLurv, the last two having been made at Ottawa 

 in 1912, and published in The Astrophysical Journal for 

 March. 



Table 40 gives the smoothed mean values of the 

 three determinations for each five degrees of solar latitude. 

 They are smoothed by the formula 10°-31+4°-03 cos 2 

 latitude. The values from sun-spots (due to Adams) are 

 given for comparison, also the times of sidereal rotation of 

 different zones. 



Table 40. 



There seems to be no clear evidence of different rates from 

 the lines of different elements, such differences as are found 

 being comparable with the probable errors. 



Carrington's adopted period for the sidereal rotation is 

 25-38 days, which corresponds with latitude 14° 6'. His 

 values for 45° and 50° are from too few spots to be reliable. 



ULTRA-NEPTUNIAN PLANETS.— I have read with 

 interest Mr. Ling's paper on this subject in the May number, 

 page 171. There are two little points on which I desire to 

 comment. First, at the end of his paragraph (2) he implies 

 that a planet of mass five times the Earth's, at a distance 

 fifty-two, would not sensibly perturb Uranus. But, as Dr. 

 Cowell pointed out, the perturbations which one planet pro- 

 duces on another depend only on the mass of the first and the 

 ratio of the distances of the two planets from the Sun ; 

 consequently a planet of mass five times ours would produce 

 the same perturbations (in heliocentric longitude) on Uranus 

 that our Earth would on Mercury if our mass were increased 

 fivefold ; but even the present perturbations of the Earth on 

 Mercury are sensible, so that those of the fivefold Earth would 

 be readily so; in the case of planet O and Uranus the 

 slower motion and the longer time for perturbations to 

 accumulate make up for the increased distance between the 



planets. Again, on page 172 he says that an unexplained 

 rotation of the major axis of the orbit of Halley's Comet 

 undoubtedly exists. If he compares the predicted elements of 

 the orbit with the observed ones he will see that they accord 

 within a few seconds. The discordance of two days does not 

 arise from a rotation of the orbit, but from an alteration in 

 the comet's mean anomaly. 



OBITUARY. — I have heard with regret of the death of 

 Professor F. W. Ristenpart, Director of the Observatory of 

 Santiago, Chili. When in Berlin he commenced and partially 

 carried out a very useful work, the combining of all star 

 catalogues into one great catalogue, with determination of 

 proper motions. He discovered a great many errata in the 

 catalogues in the course of his work, and these have already 

 been circulated. He went to Santiago about four years ago. 

 Some interesting observations of his have been published, 

 notably the organising of the observers who watched the 

 occultation of a small star by Ganymede, also good series of 

 observations of Encke's and other comets. He has lately 

 made an attempt to induce astronomers to adopt 1925 as the 

 epoch for all star places deduced up to 1950; for this purpose 

 he has published tables for reducing places from each year 

 to 1925. 



THE ORBIT OF SCHAUMASSE'S NEW COMET.— 

 Messrs. Kiess and Nicholson have found these elements: — 

 Perihelion passage, 1913, May, 17-91 G.M.T. ; Omega, 57°28'; 

 Node, 317°0'; Inclination, 153°34'. Perihelion distance, 

 1-440. Ephemeris for Greenwich — Midnight, May 27th, 

 R.A. 18 h 22 m 8", N.Dec. 35°4l'; May 31st, R.A. 17 h 22 m 42 s , 

 N.Dec. 39°5l'; June 4th, R.A. 16 h 19 m 13", N.Dec. 41°40'; 

 June 8th, R.A. 15 h 21 m 52", N.Dec. 41°ll'; June 12th, 

 R.A. 14 h 35 m 48 s , N.Dec. 39°17' ; June 16th, R.A. 14 h l' n 24 s , 

 N.Dec. 36°47'; June 20th, R.A. 13 h 35 m 56", N.Dec. 34°16'. 

 Nearest earth May 31st, when the distance is sixty-two 

 million miles ; it will probably then be of the eighth 

 magnitude. 



BOTANY 



By Professor F. Cavers, D.Sc, F.L.S. 



CLIMATE CHANGE AND WOODLAND SUCCES- 

 SION. — In an interesting paper the Rev. E. A. Woodruffe- 

 Peacock (Joiim. of Bot., 1912) claims that historical records 

 of the former occurrence of vineyards in Southern England 

 are indicative of a warmer climate. Other evidence is seen 

 in the more open texture of oaks and pines found in the older 

 peat deposits as compared with the closer texture of the 

 stems found in the more recent peat. The peat deposits of 

 East Anglia are regarded as having developed in relation to 

 woodlands on adjoining higher lands, and the tree-remains 

 represent phases of migration of woodland on to the peat. It 

 is suggested in a general way that the tree-remains represent 

 periods — oak being the oldest"; ash, holly and elm the more 

 recent. On historical, floristic and faunistic grounds the 

 Scots pine may have always been indigenous in parts of 

 Lincolnshire, as also the beech, which comes in a later period 

 with a warmer climate. 



A BRITISH FOSSIL SELA GIN ELLA.— Professor 

 Seward (New Phytologist, March, 1913) describes a fossil 

 Selaginella (Selaginellites Dawsoni) found in beautiful 

 preservation in the Fairlight Clay at the base of the Wealden 

 series at Ecclesbourne on the Sussex coast. The fact that 

 the genus Selaginella is now represented in the British flora 

 by a single species (S. spinosa), somewhat rare and chiefly 

 confined to hill regions, adds interest to this discovery of a 

 Wealden species which differs from S. spinosa, but shows a 

 close resemblance to the widely distributed recent species 

 S. rupestris — not found in Europe, however. The vegetative 

 parts are not sufficiently well preserved to show with certainty 

 whether the fossil species had one or two forms of foliage 

 leaves, but the two kinds of spores are extremely well 

 preserved and show the most minute markings on the spore 

 coat with great clearness. 



